Tools for performing voice-leading analysis with trees.
A horizontality of consecutive PitchedTimespan objects.
It must be initiated with a list or tuple of Timespan objects.
Horizontality read-only properties
Is true if the Horizontality contains a neighbor tone.
Is true if the Horizontality contains no motion (including enharmonic restatements)
Is true if the Horizontality contains a passing tone; currently defined as three tones in one direction.
(TODO: better check)